Beer, carbonated and non-carbonated soft drinks, and fruit juices (hereinafter referred to generically as beverages) are often packed in containers made from aluminum, tin-free steel, blackplate or tinplate, which is cold rolled steel to which a thin layer of tin is applied. Many of these beverages exert corrosive action upon the metal and in order to adequately protect the container and to prevent contamination of the packaged material, a sanitary liner must be applied to the internal surface of the container. However, the use of such liners also presents several problems, one of the most troublesome being the residual turbidity and taste which tends to result from some liner materials.
Because of their relatively taste-free characteristics, vinyl polymers based on vinyl chloride have been extensively employed in sanitary liners in contact with beverages. While such vinyl polymers have been useful in the past, they possess a serious disadvantage which diminishes their usefulness as sanitary liners at the present time. Thus, these vinyl polymers are generally applied from volatile organic solvent solutions at relatively low solids contents and these solvent rich solutions either add to hydrocarbon air pollution or require expensive control equipment.
In recent times, the increased emphasis on safety and environmental pollution problems have resulted in a need for water-based compositions for such liners. By "water-based" it is meant compositions in solvents comprised predominantly of water, thus greatly reducing the handling and emissions of organic solvent vapors. However, the types of solvent-based sanitary liners known and used heretofore are not obtainable as satisfactory water-based systems; indeed, it has been found that water-based materials as a class generally provide liners which impart undesirable turbidity and taste characteristics to beverages, even when the other necessary properties of such liners can be obtained.
The combination of properties which is necessary to successful utilization of any composition for container liners, and which has not been satisfactorily obtainable in water-based sanitary lining compositions known heretofore, includes the following: